Amygdala Vegetariana

In Short Cuts, the "vegetarians and vegans are more empathetic" neuroimaging article was mentioned in passing, but I didn't actually blog about it. However, there has been one thing [OK, more than one thing] bothering me about this paper...

But first, a quick summary of the Methods which were rather straightforward.

Filippi and colleagues (2010) recruited 20 omnivores, 19 vegetarians, and 20 vegans to participate in a study that examined their brain responses to images of human and animal suffering. They were naïve as to the goals of the experiment. Before entering the scanner, all participants completed the Empathy Quotient, a 40 item questionnaire [plus 20 filler questions] that rates one's level of empathy (Baron-Cohen & Wheelwright, 2004). The omnivores did indeed have lower EQ scores (38.8) than the vegetarians (49.5) and the vegans (44.6), who did not differ from each other.

The fMRI experiment used an...

...event-related design during observation of negative affective pictures of human beings and animals (showing mutilations, murdered people, human/animal threat, tortures, wounds, etc.). Participants saw negative-valence scenes related to humans and animals, alternating with natural landscapes.

So what were the neuroimaging findings? To no one's surprise, results indicated differences between the groups, as shown below.


Figure 3. Results of the between-group comparisons of emotional (human and animal) negative valence picture views. Results are superimposed on a high resolution T1-weighted image in the standard MNI space, at a threshold of p less than 0.05 corrected for multiple comparisons. Areas activated during human picture view in vegetarians and vegans vs. omnivores are shown in yellow. Activations specific for vegetarians are shown in blue. Activations specific for vegans are shown in red. A: human picture view; B: animal picture view. [NOTE: I've labeled the corpus callosum.]

Also to no one's surprise, differences between the groups were more pronounced for animal pictures (Fig. 3B) than for human pictures (Fig. 3A).

Some of the results were interpreted in Rorschach inkblot fashion: the authors saw want they wanted to see in them. Since when are the specific regions of the anterior cingulate cortex (ACC) and the inferior frontal gyrus (IFG) shown above primarily known as "empathy-related regions"? They're not.¹

...vegetarians and vegans have constantly an higher engagement of empathy related areas while observing negative scenes, independently of the species of the individuals involved, which is characterized by an increased recruitment of the ACC and the IFG. Increased activation in the ACC and left IFG in vegetarians and vegans during human and animal suffering view is likely to reflect a stronger empathic response in the first two groups.

Curiously enough, the amygdala (a limbic structure important for emotion) was not activated by animal suffering in either the vegetarians or the vegans. Although the amygdala (LeDoux, 2007) is predominantly known for its role in fear conditioning, it is also activated by other emotional responses including disgust (e.g., Kober et al., 2008).

Remarkably, the within-group analysis during animal picture view, showed the absence of signal changes (in terms of activations and deactivations) within the amygdala in vegetarians and vegans, suggesting a down-regulation of amygdala response from areas located in the frontal lobes, in an attempt to regulate emotion through cortical processes in these subjects.

Why would the vegetarians and vegans attempt to down-regulate their emotional responses to animal suffering? And why would the vegans show greater amygdala responses to human suffering than did the omnivores and vegetarians??


Figure 4. Interactions between stimuli (animal/human) and groups (omnivore/vegetarian/vegan). (A) An interaction was found in the right amygdala, indicating greater increase to animal negative valence picture view in omnivores and to human negative valence picture view in vegans. An interaction between “human pictures” and “vegan group” was also found in the left amygdala.

Previously, NeuroKüz mentioned some objections to the study design in a post on The empathetic vegetarian brain.² I won't detail his critique here other than to summarize:

• The control condition consisted of “neutral” scenes that did not include living beings, faces, or suffering of any kind.
• Participants passively viewed the photos, they did not have to respond by indicating their emotional reactions.
• Participants could be desensitized to human suffering by watching the news.

One of the greatest issues, in my view, is with the mode of stimulus presentation. The event-related design (which is usually preferable) may not have allowed adequate time between pictures to "recover" from the shock of seeing a mutilated human or animal. If this were especially true for vegetarians and vegans viewing images of animal suffering, it could explain the curious silence of the amygdala. In such scenario, a blocked design (presenting all stimuli of one category in blocks, rather than intermixed) might have been a better idea.

The vegetarians and vegans in this study all made their dietary choices for ethical reasons. It is quite conceivable that they differed from the omnivores on any number of other dimensions. For example, evolutionary psychology extremist Satoshi Kanazawa recently blogged about Why Vegetarians Are More Intelligent than Meat Eaters, but this only held for a UK sample born in 1958, but not for a US sample born between 1974 and 1983. In addition, some militant vegan PETA-types condone violence against scientists performing animal experiments, so one could expect their responses (and empathy) towards human suffering to be diminished [NOTE: empathy scores were numerically lower for vegans than for vegetarians].

It would be interesting, then, to compare these "ethical" sorts to others who have chosen to be vegetarian or vegan for heath reasons, such as familial hypercholesterolemia or athletic competitions such as the triathlon.


Left: Ma Po Tofu with Steamed Broccolini

Footnotes

¹ Compare anterior cingulate cortex, empathy to anterior cingulate cortex, cognitive control.

² Here's an even newer post, Empathy is What Really Sets Vegetarians Apart (at least Neurologically Speaking).

References

Baron-Cohen S, Wheelwright S. (2004). The empathy quotient: an investigation of adults with Asperger syndrome or high functioning autism, and normal sex differences. J Autism Dev Disord. 34:163-75.

Filippi, M., Riccitelli, G., Falini, A., Di Salle, F., Vuilleumier, P., Comi, G., & Rocca, M. (2010). The Brain Functional Networks Associated to Human and Animal Suffering Differ among Omnivores, Vegetarians and Vegans PLoS ONE, 5 (5) DOI: 10.1371/journal.pone.0010847

Kober H, Barrett LF, Joseph J, Bliss-Moreau E, Lindquist K, Wager TD. (2008). Functional grouping and cortical-subcortical interactions in emotion: a meta-analysis of neuroimaging studies. Neuroimage 42:998-1031.

LeDoux J. (2007). The amygdala. Current Biology 17: R868-R874.

Stolen from here.